[The neuroendocrine regulation of plasma corticosterone rhythm in rats]

The purpose of this study is to clarify the central mechanism of food-associated circadian oscillation whereby the prefeeding peak of plasma corticosterone was generated. Adults male rats were subjected to restricted daily feeding in which rats had free access to food at a fixed time of day. The developmental process, the oscillatory nature and the neuroendocrine control of the prefeeding corticosterone peak were investigated. The results were as follows: 1) The prefeeding corticosterone peak was established about one week after the start of restricted feeding. 2) The prefeeding peak persisted for at least 13 days even after the feeding schedule was terminated. 3) Corticotropin releasing hormone in the paraventricular nucleus (PVN) and the lower part of medial basal hypothalamus (MBH) decreased prior to daily feeding and increased postprandially under the restricted feeding. 4) Under restricted daily water supply with free access to food the prefeeding corticosterone peak was not as marked as under the restricted feeding. 5) Plasma arginine vasopressin (AVP) seemed not be involved in the generation of prefeeding corticosterone peak. 6) The prefeeding corticosterone peak failed to appear in the VMH-isolated rats in the dynamic phase, while it appeared in the static phase. These results indicate that the prefeeding corticosterone peak is regulated by an oscillatory mechanism, but are not consistent with the hypothesis that VMH is a site of the oscillation. The present results suggest that the energy state influences the expression of the prefeeding corticosterone peak.